The present invention relates to brakes for example for motor vehicles, of the kind in which the braking surfaces are formed on the axially--extending internal and external surfaces of a drum. Such brakes are generally referred to as "internal-external shoe drum brakes" or as "crown brakes". The latter term is used herein.
A brake of this kind comprises a fixed bracket, adapted to be attached to any support element, e.g. the journal of a braked wheel, to the shaft of which the corresponding drum or "crown" is keyed, two brake shoes arranged each respectively on either side of the crown, and control means adapted to act on said brake shoes to apply them to the braking surfaces formed on either side of the crown, the shoes being applied in a generally radial direction known as the clamping axis passing through the median zone of each of the brake shoes.
The present invention deals more particularly with the case in which the control means includes a generally C shaped control piece, commonly called the calliper, which extends radially on either side of the crown and of the brake shoes, and which exhibits, at the ends of a median part joining them mutually, on the one hand a first wing which is equipped with a clamping element whereby it can act upon a first of said brake shoes, and on the other hand a second wing, whereby it can act upon the second brake shoe, said control part being mounted to be radially movable in relation to the crown and being provided laterally for that purpose at least one guide lug, by the aperture of which it is engaged on a guide pin integral with the fixed bracket.
One difficulty which has to be overcome in the brakes of this kind results from the necessity to fulfil simultaneously two requirements; these are firstly to ensure with full security an appropriate lubrication of the calliper with reference to its guide pin or pins, in order to prevent incorrect sliding of said calliper on said pin or pins, which might prevent after braking, a proper withdrawal of the brake shoes with reference to the crown and thus lead to the untimely perpetuation of a residual braking torque generating more rapid wear of the brake shoes, and secondly to ensure easy access to the brake shoes for simple and rapid replacement thereof after wear.
Since access to the brake shoes generally implies the previous removal of the calliper, these two requirements are to some degree contradictory, since the achieving of good guidance of the calliper and of good conditions of lubrication for the corresponding sliding surfaces assumes the use of means leading to a confinement of the calliper by the fixed bracket, and therefore normally preventing the easy withdrawal of said calliper with reference to said fixed support.
It is a broad object of the invention to provide an arrangement which permits both the requirements in question to be satisfied in a simple and efficacious manner.